As the trend toward mechatronic integration continues there is increasing use of electronics and sensors at significantly higher ambient temperatures/thermal power losses under simultaneously very harsh application or environmental conditions. In the field of high-temperature electronics in particular, this requires hermetically sealed, robust and integratable connections to the outside world to be provided in a minimum of installation space. At temperatures above 150° C., electrical feedthroughs in plastic packages are often suitable only to a limited extent. Studies show that at 180° C. first failures of the circuits integrated in the plastic package will occur already within 250 hours. Known electrical metal-glass feedthroughs are frequently problematic in terms of manufacturability, in particular in terms of planar manufacturing methods and thermal adaptation, and with regard to integration into the package.
Glass feedthroughs have been used in electrical feedthroughs in metal packages, as provided for example with kovar (kovar denotes alloys having a low coefficient of thermal expansion, typically approx. 5 ppm/K, which is therefore lower than the coefficient for metals; composition e.g. 54% iron, 29% nickel and 17% cobalt; other compositions are also possible). The package is then sealed by a cover which generally is welded using a roll seam. In ceramic packages, use is made of ceramics sintered in multilayer technology and having metallized current feedthroughs. In such an arrangement a cavity is provided for mounting of the chip and for the wiring by bonding. Typically, the cover has to be soldered, in particular using inert protective gas, without the use of flux, with gold surfaces being used. Molded metallic frames/leadframes are often used in electrical feedthroughs in plastic packages. In terms of the necessary hermiticity and due to the mechanical stresses occurring, encasements made of plastic can only be used to a limited degree for higher temperatures.
“A Tenfold Reduction in Interface Thermal Resistance for Heat Sink Mounting” D. Van Heerden, O. M. Knio, and T. P. Weihs; Reactive Nano Technologies, 111 Lake Front Drive, Hunt Valley, Md. 21030 (“Van Heerden et al.”), discloses a tenfold reduction in the thermal resistance of an interface for heat sink mounting. The company “Reactive Nano Technologies (RNT)” has developed a new platform joining technology that can form a metallic bond between a chip package and a heat sink and at the same time offer a thermal interface resistance that is ten times lower than that of current thermal interface materials (TIMs). The joining process is based on the use of reactive multilayer foils as local heat sources. The foils are a new class of nano-engineered materials in which self-propagating exothermic reactions can be initiated at room temperature by a hot filament or laser. When a multilayer foil is inserted between two solder layers and a chip package and heat sink, heat generated by a chemical reaction in the foil heats the solder to melting point and consequently bonds the components. The joining process can be completed in air, argon or vacuum in approximately one second. The resulting metallic joints exhibit thermal conductivities that are two orders of magnitude higher and thermal resistivities that are an order of magnitude lower than current commercial thermal interface materials (TIMs). It is demonstrated using numeric models that the thermal exposure of microelectronic packages during joining is very limited. Finally it is shown numerically that reactive joining can be used to solder silicon dies directly to heat sinks without thermally damaging the chip.
“Direct Die Attach With Indium Using a Room Temperature Soldering Process” J. S. Subramanian, T. Rüde, J. Newson, Z. He, E. Besnoin, T. Weihs; Reactive Nano Technologies, 111 Lake Front Drive, Hunt Valley, Md. 21030, discloses a direct die attach technique with indium using a room temperature soldering process. A new joining process is described which allows fluxless, lead-free soldering at room temperature through the use of reactive multilayer foils as a local heat source. Activating a multilayer foil between solder layers on components causes heat to be generated due to a reaction within the foil. This process provides sufficient localized heat to melt the solder and bond the components together. The use of this foil to enable silicon dies to be attached directly to thermal management components is presented. Results of the modeling system for predicting temperatures at various interfaces during the joining are shown and verified. In the final section, data on thermal performance is provided which indicates that a six- to eightfold improvement on die sizes from 8×8 mm to 17.5×17.5 mm is made possible.